There are several contemporary cyanoacrylate-based wound closures that exist today, including, for example, Dermabond®, Indermil®, and Histoacryl®. Dermabond® topical skin adhesive (2-octyl cyanoacrylate) is a sterile, liquid skin adhesive that holds wound edges together and is available from Ethicon US LLC, a Johnson & Johnson company. Dermabond® (a registered trademark of Johnson & Johnson Company, New Brunswick, N.J., or more particularly, 2-octyl cyanoacrylate works as a very low viscosity liquid monomer, which, when applied to the skin over the wound, rapidly (i.e., within seconds to minutes) polymerizes and forms a stiff, transparent protective coating. The polymerization is initiated by moisture on the skin or nucleophilic (e.g., —OH and —NH2) groups on the surface of the skin. Thus the -CA groups become chemically attached or bound to the skin such that the resultant poly(2-octyl cyanoacrylate) coating, in fact, becomes a chemical part of the skin.
Indermil® tissue adhesive (N-butyl-2-cyanoacrylate) is another wound closure product similar to Dermabond®, but is available from Covidien Co., a Henkel company. Indermil® is a registered trademark of Henkel Corporation, Rocky Hill, Conn. Histoacryl® topical skin adhesive (N-butyl-2-cyanoacrylate) is also a skin adhesive available from B. Braun Corporation. Histoacryl® is a registered trademark of Aesculap, Inc., Center Valley, Pa. Both of these adhesives are based upon the N-butyl-2 cyanoacrylate which chemically differs from 2-octyl cyanoacrylate.
However, each of these contemporary cyanoacrylate-based products has its drawbacks. For instance, all of these products produce stiff films or coatings upon polymerizing shortly after application and, therefore, have the problem of sloughing off easily after application and drying, particularly when the skin is in motion. Thus Dermabond® and the other contemporary cyanoacrylate-based wound closures or adhesives cannot be applied where the skin is in frequent motion, i.e., over the elbow, knee, knuckles, wrist, face, etc. Application at these sites would require a flexible or rubbery wound cover. Furthermore, each of these products is not oxygen permeable or breathable and, therefore, is a barrier to oxygen necessary for healing of the skin. Still further, many of these contemporary cyanoacrylate-based wound closures and adhesives are occlusive, meaning they do not allow the evaporation of water vapor caused by exudates within the wound during the healing process. Again, this prevents or delays the healing of the wound.
Still other deficiencies of one or more of the contemporary cyanoacrylate-based wound closures or adhesives are the low viscosity of some of the liquid forms. For example, Dermabond® has a low viscosity and is therefore “runny”. It is well known to travel uncontrollably and rapidly over surfaces and enters into cuts or wounds where it polymerizes. Because it cannot be completely controlled and polymerizes rapidly (within seconds or minutes), it becomes a stiff polymer over the wound. Because it is not breathable, it further delays healing of the wound. This may also be an issue should the product get under the skin. While the toxicity of Dermabond® is sufficiently low to be used on the surface of the skin, it is still inappropriate for under-the-skin use and cannot be used for subcutaneous applications such as, for example, for use as implantable anti-adhesive for organ coatings.
With respect to the problem of stiffness, attempts have heretofore been made to address this issue. Contemporary research has reduced to practice polyisobutylenes endowed with or functionalized with cyanoacrylate groups (PIB-CA), which provide significantly improved flexibility over the contemporary cyanoacrylate-based products mentioned hereinabove. Such cyanoacrylate-functionalized polyisobutylenes have been used to provide flexible transparent wound closures with good mechanical properties with respect to tensile strength and elongation. However, like the contemporary cyanoacrylate-based wound closures and adhesives above, these polyisobutylene-based wound closures are not breathable and are barriers to gases and vapors (moisture) so as to not allow for the evaporation of exudates within the wound. Thus, it is well known that polyisobutylene is used as flexible air-and-moisture impermeable skin adhesives and closures, for example, as a constituent in colostomy patches.
There are also a number of medical grade silicone adhesives on the market today. However, some of these silicone adhesives, such as SILASTIC® Medical Adhesive Silicone, Type A, are used to bond elastomers, synthetics and metals for part fabrication and medical devices. They are not used as wound closures or wound adhesives and do not contain cyanoacrylates. SILASTIC® Medical Adhesive Silicone, available from Dow Corning Corporation, is a one-part, low-slump, translucent silicone material that is solventless and cures at room temperature between 50-60% relative humidity. SILASTIC® is a registered trademark of Dow Corning Corporation, Midland, Mich. There are also silicone adhesive tapes available on the market today. An example of such a product is 3M™ Kind Removal Silicone Tape, available from 3M Corporation, St. Paul, Minn. Again, such silicone adhesive tapes also do not contain cyanoacrylates and are used to adhere various tubes and instruments to the skin, such as IVs and the like. They are not used as wound closures or wound adhesives.
Further, it should be understood that there are a line of products available on the market today that are called “silicone adhesives” or “silicone rubber adhesives” that are not made of silicone rubbers at all. Instead, these products are used to bond silicone rubber to other things such as metal, synthetic, or other rubber products. That is, they are named after that to which they adhere, not that of which what they are made.
There are, however, at least a few wound dressing products that contain silicone rubber or silicone rubber foams on account of silicone's biocompatibility, appropriate mechanical properties, rubbery nature (flexibility), oxygen and gaseous water (vapor) permeability, optical transparency, and good “feel” on the skin. However, none of these silicone rubber-based products contain cyanoacrylates. In fact, many of them use polyurethane foam dressings with silicone adhesives for securing the foam dressing to the skin. Thus, the silicone adhesives are used in conjunction with additional layers for providing therapy to the wound.
There are literally hundreds of wound closure products on the market. A closer examination, however, reveals that the active constituents of these products are only a few, and the products differ only in name, appearance, and shape (marketing strategies). Most of these products are above, and a more detailed description of these products may be found in the books “Clinical Guide to Skin and Wound Care” (7th edition) by A. T. Hess, Wolters Kluwer Pub., 2013, and “Wound Care” (4th edition) by C. Sussman and B. Bates-Jensen, Wolters Kluwer Pub, 2012.
Thus, a need exists for a flexible, transparent polymeric composition that can be used as a wound closure, adhesive, sealant or skin protectant. Such a composition desirably includes all of the benefits of a cyanoacrylate-based composition, including its instantaneous adhesion to skin and its protective coating properties, as well as all of the benefits of a silicone rubber-based composition, including its biocompatibility, appropriate mechanical properties, rubbery nature (i.e., flexibility), oxygen and gaseous water (vapor) permeability, optical transparency, and good “feel” on the skin.